The discussion of the background of the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge at the priority date of any of the claims.
An ophthalmic lens is typically made of plastic or glass material and generally has two opposing surfaces which co-operate to provide a required corrective prescription. When the positioning or shape of one of these surfaces with respect to the other is inaccurate, optical errors can occur.
Manufacturing of an ophthalmic lens to the required prescription requirements typically includes machining a face of a semi-finished lens. Typically, a semi-finished lens has a finished face, for example the front face and an unfinished face, for example the back face. By machining the back face of the lens to remove material, the required shape and positioning of the surface of the back face with respect to the surface of the front face for the desired corrective prescription can be generated.
Conventionally, the surface of the finished face of the semi-finished lens is obtained by molding.
The surface of the finished face is provided with engraved markings on the finished face. The engraved markings define a reference system of the surface of the finished face of the semi-finished lens.
The finished face of the semi-finished lens and the engraved markings are obtained by injecting an optical material in a specific mold.
The internal surface of the specific mold is arranged so as to provide the finished face of the semi-finished lens and the corresponding markings.
Since the corresponding markings are used as reference markings during the manufacturing of the optical lens, the position of such markings is required to be very accurate, thus increasing the price of the molds and of the overall process.
Furthermore, during the molding process, the lens member material is injected in the mold after having been heated and is cooled to solidify in the mold. During the cooling step, the material may deform creating an uncertainty on the positions of the reference markings.